Characterisation of Residues and Extracts of High-Pressure Extraction of Eucalyptus Wood by 1,4-Dioxane-CO2 Mixtures. Part I. Characterisation by FTIR, UV and HPLC

Abstract

In this work residues and extracts resulting from high-pressure extractions of Eucalyptus globulus Labill. by 1,4-dioxane and 1,4-dioxane-CO 2 mixtures, in the temperature range 160°C-180°C at 170 bar and 250 bar pressures were characterised by spectroscopic and chromatographic techniques. Spectral data of extraction residues showed that thermal degradation starts to occur at 180°C. At lower temperatures cellulose is neither degraded nor extracted and changes in intensity of FTIR absorption bands indicate lignin and hemicellulose extraction. Hemicellulose removal is an essentially degradative process. The FTIR spectra of lignins recovered from extraction liquors show absorption bands with very well defined peaks. They are very similar to literature data obtained for hardwood lignins extracted in mild conditions. Namely, all the absorption bands observed in milled wood lignins of GS3-GS4 types are visible. Acid soluble residual lignins appear to be rich in guaiacyl units, while UV and FTIR spectra show that extracted lignins are rich in syringyl units.